The invention relates to electro-optical liquid-crystal displays, and more particularly, mediums for such displays.
In conventional liquid-crystal displays (TN, STN, OMI AMD-TN), the electric fields for the re-alignment are generated essentially perpendicular to the liquid-crystal layer.
International Patent Application WO 91/10936 discloses a liquid-crystal display in which the electric fields have a significant component parallel to the liquid-crystal layer (IPS, in-plane switching). The principles of operation of a display of this type are described, for example, by R. A. Soref in Journal of Applied Physics, Vol. 45, No. 12, pp. 5466-5468 (1974).
For example, EP 0 588 568 discloses various possibilities for designing the electrodes and for addressing a display of this type.
Compounds of the formula 
in which R=alkyl are disclosed in EP 0 019 665 and U.S. Pat. No. 4,455,261.
However, there is no indication therein that the properties of IPS displays can be improved with the aid of these substances.
IPS displays containing liquid-crystal media including a compound of the formula 
and compounds of the formula 
have already been mentioned in DE 198 48 181. However, the liquid-crystal media achieved therein have only inadequate dielectric anisotropy values and excessively low clearing point values.
These IPS displays can be operated with liquid-crystalline materials of either positive or negative dielectric anisotropy (xcex94xcex5xe2x89xa00). However, the materials disclosed hitherto generally give not only poor low-temperature storage stabilities and long response times in IPS displays, but in addition the liquid-crystalline materials have excessively high birefringence values, inadequate voltage holding ratios and, in particular, excessively low clearing point values and very particularly excessively low dielectric anisotropy values.
In particular the combination of high dielectric anisotropy, for achieving a relatively low threshold, with a high clearing point was desirably needed without severe impact on the voltage holding ratio, the low-temperature stability and the response time.
As used herein, the terms xe2x80x9cincludexe2x80x9d or xe2x80x9chavexe2x80x9d mean to take in, enfold, or comprise as a discrete or subordinate part or item of a larger aggregate, group or principle.
Surprisingly, this feature has been achieved by using liquid-crystalline materials which can include at least two compounds of the formula I, at least one compound of the formula II and/or at least one compound of the formula III and/or IV.
The IPS mixtures according to the invention can improve over the prior art by their relatively high clearing points and low rotational viscosity values and their increased stability to crystallization at low temperatures.
The invention thus generally relates to an electro-optical liquid-crystal display having a re-alignment layer, for re-aligning the liquid crystals, including a field having a significant component parallel to the liquid-crystal layer, including a liquid-crystalline medium of positive dielectric anisotropy, where the medium includes one or more compounds of the formula I and one or more compounds selected from the group of compounds of the formulae II and III 
in which
R1, R2 
and R3 are each, independent of one another,
alkyl or alkoxy having 1 to 7 carbon atoms or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 7 carbon atoms,
Y11, Y12, Y21 Y22,
Y31 and Y32 are each, independent of one another, H or F, 
are each, independent of one another, 
xe2x80x83and
Qxe2x80x94X is F, Cl, xe2x80x94OCF2H or xe2x80x94OCF3.
R1 is particularly preferably ethyl, n-propyl and/or n-butyl.
The liquid-crystalline medium preferably includes two or more, particularly preferably three, four or more, most preferably three, compounds of the formula Ia 
which R1 is as defined under the formula I and is preferably ethyl, n-propyl, n-butyl or n-pentyl, particularly preferably ethyl, n-propyl or n-pentyl.
In addition to the compounds of the formula Ia, the medium preferably includes one or more compounds selected from the group of compounds of the formulae IIa to IIc 
particularly preferably one or more compounds of the formula Ia, very particularly preferably one or more compounds of the formula IIc,
in which R2 is as defined above under the formula II, and
particularly preferably in each case one or more compounds of the formulae Ia and IIc and/or
one or more compounds from the group of the formulae IIIa to IIII 
in which R3 is as defined above for R1 under the formula I and is preferably ethyl, n-propyl, n-butyl or n-pentyl, particularly preferably ethyl, n-propyl or n-pentyl.
Preference is given to liquid-crystal displays having liquid-crystalline media including one or more compounds of the formula IV 
in which
R4 is H, an alkyl or alkenyl radical having 1 to 15 carbon atoms which is monosubstituted by CN or CF3 or at least monosubstituted by halogen, preferably by F, where, in addition, one or more CH2 groups in these radicals may each, independently of one another, be replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, 
xe2x80x83xe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94Oxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94 in such a way that O atoms are not linked directly to one another,
A41, A42 
and A43 are each, independent of one another,
(a) a trans-1,4-cyclohexylene radical, in which, in addition, one or more non-adjacent CH2 groups may be replaced by xe2x80x94Oxe2x80x94 and/or xe2x80x94Sxe2x80x94,
(b) a 1,4-phenylene radical, in which, in addition, one or two CH groups may be replaced by N,
(c) a radical from the group consisting of 1,4-cyclohexenylene, 1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl,
where the radicals (a) and (b) may be substituted by one or two fluorine atoms,
Z41, Z42 
and Z43 are each, independent of one another, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94 or a single bond, or one of the radicals Z41 and Z42 is alternatively xe2x80x94(CH2)4xe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94CH2CH2xe2x80x94,
X4 is F, xe2x80x94OCF2H or xe2x80x94OCF3, preferably F or xe2x80x94OCF3,
Y41 and Y42 are each, independent of one another, H or F, and
n1 and n2 are each, independent of one another, 0 or 1.
In a preferred embodiment, the liquid-crystal displays contain liquid-crystalline media comprising three or more compounds of the formula I, particularly preferably in which R1 is ethyl, n-propyl or n-butyl, and one or more compounds of the formula IVa and one or more, preferably two or more, compounds of the formula IIId 
in which R4 is in each case as defined above under the formulae IVa and IIId, but is preferably ethyl, n-propyl, n-butyl or n-pentyl, particularly preferably ethyl or n-propyl.
In another preferred embodiment, the liquid-crystal display can include a liquid-crystal medium which predominantly, virtually exclusively or exclusively includes, as dielectrically positive compounds, i.e. as compounds having a xcex94xcex5 of greater than about +1.5, determined by extrapolation from the data of a mixture of about 15% of the substance in the mixture ZLI-4792 from Merck KGaA, compounds of the formulae I, II and III. In this application, xe2x80x9cpredominantlyxe2x80x9d means that the proportion of corresponding other compounds (here, for example, other compounds having xcex94xcex5 greater than  about +1.5) in the mixture as a whole is less than about 10%, xe2x80x9cvirtually exclusivelyxe2x80x9d means that this proportion is less than about 5%, and xe2x80x9cexclusivelyxe2x80x9d means that this proportion is less than about 1%. The liquid-crystal displays very particularly preferably can include absolutely no compounds having xcex94xcex5 greater than  about 1.5 other than those of the formulae I, II and III.
In this embodiment, the liquid-crystal mixtures can include
preferably two, three or four, particularly preferably three, compounds of the formula I, particularly preferably of the formula Ia, and
two, three or four, particularly preferably two or three, compounds of the formula II, preferably one or more compounds of the formula Ia and one or more compounds of the formula IIc and
one or more, preferably two or more, compounds of the formula III, particularly preferably of the formula IIIa.
Preference is furthermore given to liquid-crystal displays in which the liquid-crystalline medium can include one or more compounds of the formula V 
in which
R51 and R52 are each, independent of one another, having the meaning of R4 as described above in formula IV,
A51, A52, A53 and A54 each, independent from one another, has the meaning of A41 under formula IV above,
Z51, Z52 and Z53 each, independent from one another, has the meaning of Z41 under formula IV above
l1, and l2 are each 0 or 1,
and preferably
l1+l2 is 0 or 1.
In a preferred embodiment, the liquid-crystal displays generally include liquid-crystal mixtures including one or more compounds of the formula IId 
in which R2 is as defined above under the formula II and is preferably n-alkyl having 2 to carbon atoms, in particular ethyl, propyl and/or butyl.
The liquid-crystal displays preferably include liquid-crystal mixtures having
one or more compounds of the formula IIa in which Y21=Y22=H,
one or more compounds of the formula Ia in which Y21=Y22=F,
both one or more compounds of the formula IIa in which Y21=Y22=F and one or more compounds of the formula IIa in which Y21=Y22=H,
one or more compounds of the formula IIb in which Y21H and Y22=F.
one or more compounds of the formula IIa in which Y21=Y22=H and X=OCF3,
one or more compounds of the formula IIIb in which Y21=H, Y22 is H or F, and Y=F.
Preferred embodiments are furthermore IPS displays in which
the medium can additionally include one or more compounds selected from the group consisting of the compounds of the formulae Va and Vb 
xe2x80x83in which
R51 and R52 are each, independent of one another, alkyl or alkoxy having 1 to 7 carbon atoms or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 7 carbon atoms, R51 preferably being alkyl, particularly preferably having 1 to 5 carbon atoms, R52 preferably being alkyl or alkoxy, preferably alkoxy having 1 to 3 carbon atoms,
and/or from the group of the formula Vc 
in which
R51 and R52 independent of one another, are as defined above for R5 and R52 respectively under the formula Va,
R52 preferably being n-alkyl having 3 to 5 carbon atoms, and R51 preferably being 1E-alkenyl.
The liquid-crystal displays preferably have liquid-crystal mixtures including
one or more, particularly preferably two or more, compounds of the formula Va in which, preferably, at least one of the groups R51 and R52 is alkenyl, preferably 1E-alkenyl, particularly preferably vinyl or 1E-propenyl,
one or more compounds of the formula Vb in which, preferably,
R51 is n-alkyl having 3 to 5 carbon atoms, particularly preferably having 3 or 5 carbon atoms, in particular having 3 carbon atoms, and
R52 is alkoxy having 1 to 3 carbon atoms, particularly preferably having 2 carbon atoms, and
one or more, preferably two or more, compounds of the formula Vc in which
R52 is n-alkyl having 1 to 5 carbon atoms, preferably having 1 to 3 carbon atoms, and
R51 is 1E-alkenyl having 2 to 5 carbon atoms, preferably having 2 to 3 carbon atoms.
Preference can be furthermore given to an IPS display in which the pixels are addressed by means of an active matrix.
The invention furthermore relates to a liquid-crystalline medium of positive dielectric anisotropy which comprises at least one, particularly preferably at least three, compounds of the formula I and at least one compound selected from the group consisting of the compounds of the formulae IIa to IIIb, and at least one compound selected from the group consisting of the compounds of the formulae IVa and IIId, and at least one compound selected from the group consisting of the compounds of the formulae Va to Vc, in particular which comprises
from about 5-about 30, preferably from about 8-about 20, in particular from about 11-about 17, or alternatively, about 3-about 35% by weight of at least one compound of the formula I,
from about 5-about 40, preferably from about 15-about 30, or alternatively, about 2-about 45% by weight of at least one compound of the formula II, preferably of the formulae Ia to IIc,
from 0-about 20, preferably from about 5-about 15, or alternatively, 0-about 25% by weight of at least one compound of the formula III, preferably of the formula IIIa,
from 0 to 30, preferably from 0 to 25, % by weight of at least one compound of the formulae III and IV, preferably selected from the group consisting of the compounds of the formulae IVa and IIId,
from about 10 to about 70, preferably from about 30-about 60, or alternatively about 7-about 75% by weight of at least one compound of the formula V, preferably selected from the group of compounds of the formulae Va to Vc, of these preferably from about 30-about 60% by weight, particularly preferably from about 30-about 55% by weight, based on the mixture as a whole, of compounds selected from the group of compounds of the formulae Va and Vb.
In particular here, but also throughout the application, all sub-combinations of the preferred ranges are desirable.
The liquid-crystal displays according to the invention preferably include a liquid-crystalline medium having:
at least two, preferably three, compounds of the preferred formula Ia 
xe2x80x83in which
R1 is as defined above under the formula I, preferably n-alkyl.
In a further preferred embodiment, the displays according to the invention include media having one or more compounds of the formula Ia and one or more compounds of the formula IIa and one or more compounds of the formula IIc.
The liquid-crystalline media used in accordance with the invention generally have a birefringence (xcex94n) of  less than about 0.12, preferably in the range from about 0.05 to about 0.11, in particular in the range from about 0.07 to about 0.10, very particularly in the range from about 0.08 to about 0.095.
The flow viscosity (at 20xc2x0 C.) of the mixtures used in accordance with the invention is generally less than about 30 mm2xc2x7sxe2x88x921, in particular from about 15 to about 25 mm2xc2x7sxe2x88x921.
The specific resistance of the materials according to the invention at 20xc2x0 C. is generally from about 5xc3x971010 to about 5xc3x971010 xcexa9xc2x7cm, particularly preferably from about 5xc3x971011 to about 5xc3x971012 xcexa9xc2x7cm. The rotational viscosity of the mixtures according to the invention at 20xc2x0 C. is generally less than about 100 mPaxc2x7s, in particular from about 50 to about 85 mPaxc2x7s.
Media having clearing points of from about 70 to about 80xc2x0 C. used in accordance with the invention have rotational viscosities of about 120 mPaxc2x7s or less, preferably from about 80 to about 110 mPaxc2x7s.
The clearing point of the media used in accordance with the invention is above about 60xc2x0 C, preferably at least about 70xc2x0 C. and particularly preferably above about 70xc2x0 C. and up to about 90xc2x0 C. In particular, the clearing point is in the range from about 70xc2x0 C. to about 80xc2x0 C. The storage stability in test cells, determined as described below, is about 1000 hours or more at about xe2x88x9230xc2x0 C., preferably about 500 hours or more at about xe2x88x9240xc2x0 C. and very particularly preferably about 1000 hours or more at about xe2x88x9240xc2x0 C.
The liquid-crystal media according to the invention have dielectric anisotropy values of greater than about 6.5. xcex94xcex5 is preferably in the range from about 7 to about 25, particularly preferably in the range from about 9 to about 12, especially preferably in the range from about 10 to about 20, very particularly in the range from about 11 to about 13.
The media used in accordance with the invention can include of from about 5 to about 40 compounds, preferably from about 6 to about 20 compounds, particularly preferably from about 9 to about 16 compounds, and most preferably from about 11 to about 14 compounds.
It has been found that even a relatively small proportion of compounds of the formula I mixed with conventional liquid-crystal materials, but in particular with one or more compounds selected from the group consisting of the compounds of the formulae IIa to IIIb and/or from the group consisting of the compounds of the formulae IIId, IVa, Va and Vb, results in a significant reduction in the threshold voltage, in favourable values for the rotational viscosity xcex31 and in fast response times, in particular broad nematic phases having low smectic-nematic transition temperatures being observed. The compounds of the formulae I to IV are colourless, stable and readily miscible with one another and with other liquid-crystal materials.
The term xe2x80x9calkylxe2x80x9d can include straight-chain and branched alkyl groups having 1-7 carbon atoms, in particular the straight-chain groups methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups having 2-5 carbon atoms are preferred, unless explicitly stated otherwise.
The term xe2x80x9calkenylxe2x80x9d can include straight-chain and branched alkenyl groups having 2-7 carbon atoms, in particular the straight-chain groups. Particularly preferred alkenyl groups are C2-C7-1E-alkenyl, C4-C7-3E-alkenyl, C5-C7-4-alkenyl, C6-C7-5-alkenyl and C7-6-alkenyl, in particular C2-C7-1E-alkenyl, C4-C7-3E-alkenyl and C5-C7-4-alkenyl. Examples of very particularly preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3E-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups having up to 5 carbon atoms are preferred, unless explicitly stated otherwise.
The term xe2x80x9cfluoroalkylxe2x80x9d preferably covers straight-chain groups having a terminal fluorine, i.e. fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. However, other positions of the fluorine are not excluded.
The term xe2x80x9calkoxyalkylxe2x80x9d preferably covers straight-chain radicals of the formula CnH2n+1xe2x80x94Oxe2x80x94(CH2)m, in which n and m are each, independent of one another, from 1 to 6. m is preferably 1 and n is preferably from 1 to 4.
Through a suitable choice of the meanings of R1 to R51, the addressing times, the threshold voltage, the steepness of the transmission characteristic lines, etc., can be modified in the desired manner. For example, 1E-alkenyl radicals, 3E-alkenyl radicals, 2E-alkenyloxy radicals and the like generally result in short addressing times, improved nematic tendencies and a higher ratio of the elastic constants k33 (bend) and k11 (splay) compared with alkyl or alkoxy radicals. 4-Alkenyl radicals, 3-alkenyl radicals and the like generally give lower threshold voltages and smaller values of k33/k11 compared with alkyl and alkoxy radicals.
The optimum mixing ratio of the compounds of the formulae I and II+III+IV+V depends substantially on the desired properties, on the choice of the components of the formulae I, II, III, IV and/or V, and on the choice of any other components which may be present. Suitable mixing ratios within the range given above can easily be determined from case to case.
The total amount of compounds of the formulae I to V in the mixtures according to the invention is not crucial. The mixtures preferably include 50-90% by weight of compounds of the formulae I to V. The mixtures may also include one or more further components in order to optimize various properties. However, the observed effect, particularly on the level of the dielectric anisotropy, is generally greater the higher the total concentration of compounds of the formulae I to V, in particular of the formula I.
In a particularly preferred embodiment, the media according to the invention includes compounds of the formula III in which X3 is OCF3. A favorable synergistic effect with the compounds of the formulae I and II can result in particularly advantageous properties.
In addition to one or more compounds of the formula I, the liquid-crystalline media according to the invention preferably include from about 2 to about 35, in particular from about 4 to about 20, very particularly from about 5 to about 9, compounds as further constituents, not counting additives such as, for example, dyes and dopants. These media very particularly preferably include from about 7 to about 15 compounds in addition to one or more compounds of the formula I. These further constituents are preferably selected from nematic or nematogenic (monotropic or isotropic) substances, in particular substances from the classes of the azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl esters of cyclohexanecarboxylic acid, phenyl or cyclohexyl esters of cyclohexylbenzoic acid, phenyl or cyclohexyl esters of cyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl esters of benzoic acid, of cyclohexanecarboxylic acid and of cyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes, 4,4xe2x80x2-bis-cyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, phenyl- or cyclohexyldioxanes, phenyl- or cyclohexyl-1,3-dithianes, 1,2-diphenylethanes, 1,2-dicyclohexylethanes, 1-phenyl-2-cyclohexylethanes, 1-cyclohexyl-2-(4-phenylcyclohexyl)ethanes, 1-cyclohexyl-2-biphenylylethanes, 1-phenyl-2-cyclohexylphenylethanes, optionally halogenated stilbenes, benzyl phenyl ethers, tolans and substituted cinnamic acids. The 1,4-phenylene groups in these compounds may also be fluorinated.
The most desirable compounds suitable as further constituents of media according to the invention can be characterized by the formulae 1, 2, 3, 4 and 5:
Rxe2x80x2xe2x80x94Lxe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x831
Rxe2x80x2xe2x80x94Lxe2x80x94COOxe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x832
Rxe2x80x2xe2x80x94Lxe2x80x94OOCxe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x833
xe2x80x83Rxe2x80x2xe2x80x94Lxe2x80x94CH2CH2xe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x834
Rxe2x80x2xe2x80x94Lxe2x80x94Cxe2x89xa1Cxe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x835
In the formulae 1, 2, 3, 4 and 5, L and E, which may be identical or different, are in each case, independent of one another, a bivalent radical from the group formed by -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe- and -G-Cyc- and their mirror images, where Phe is unsubstituted or fluorine-substituted 1,4-phenylene, Cyc is trans-1,4-cyclohexylene or 1,4-cyclohexylene, Pyr is pyrimidine-2,5-diyl or pyridine-2,5-diyl, Dio is 1,3-dioxane-2,5-diyl and G is 2-(trans-1,4-cyclohexyl)ethyl, pyrimidine-2,5-diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl.
One of the radicals L and E is preferably Cyc, Phe or Pyr. E is preferably Cyc, Phe or Phe-Cyc. The media according to the invention preferably include one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which L and E are selected from the group of Cyc, Phe or Pyr and simultaneously one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which one of the radicals L and E is selected from the group of Cyc, Phe or Pyr and the other radical is selected from the group of -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- or -G-Cyc-, and optionally one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which the radicals L and E are selected from the group of -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- or -G-Cyc-.
In a smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5, Rxe2x80x2 and Rxe2x80x3 are each, independent of one another, alkyl, alkenyl, alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy having up to 8 carbon atoms. This smaller sub-group is called group A below, and the compounds are denoted by the sub-formulae 1a, 2a, 3a, 4a and 5a. In most of these compounds, Rxe2x80x2 and Rxe2x80x3 are different from one another, one of these radicals usually being alkyl, alkenyl, alkoxy or alkoxyalkyl.
In another smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5 which is called group B, Rxe2x80x3 is desirably xe2x80x94F, xe2x80x94Cl, xe2x80x94NCS or xe2x80x94(O)iCH3xe2x88x92(k+1)FkCl1, where i is 0 or 1, and k+1 is 1, 2 or 3; the compounds in which Rxe2x80x3 has this meaning are denoted by the sub-formulae 1b, 2b, 3b, 4b and 5b. Particular preference is given to compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b in which Rxe2x80x3 is xe2x80x94F, xe2x80x94Cl, xe2x80x94NCS, xe2x80x94CF3, xe2x80x94OCHF2 or xe2x80x94OCF3.
In the compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b, Rxe2x80x2 is as defined for the compounds of the sub-formulae 1a-5a and is preferably alkyl, alkenyl, alkoxy or alkoxyalkyl.
In a further smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5, Rxe2x80x3 is desirably xe2x80x94CN; this sub-group is called group C below, and the compounds of this sub-group are correspondingly described by sub-formulae 1c, 2c, 3c, 4c and 5c. In the compounds of the sub-formulae 1c, 2c, 3c, 4c and 5c, Rxe2x80x2 is as defined for the compounds of the sub-formulae 1a-5a and is preferably alkyl, alkoxy or alkenyl.
In addition to the preferred compounds from groups A, B and C, other compounds of the formulae 1, 2, 3, 4 and 5 having other variants of the proposed substituents may also be used. All these substances can be obtained by methods which are known from the literature or analogously thereto.
In addition to the compounds of the formula I, the media according to the invention preferably include one or more compounds selected from group A and/or group B and/or group C. The proportions by weight of the compounds from these groups in the media according to the invention are preferably
Group A: from 0 to about 90%, preferably from about 20 to about 90%, in particular from about 30 to about 90%
Group B: from 0 to about 80%, preferably from about 10 to about 80%, in particular from about 10 to about 65%
Group C: from 0 to about 80%, preferably from about 5 to about 80%, in particular from about 5 to about 50%,
the sum of the proportions by weight of the group A and/or B and/or C compounds present in the particular media according to the invention preferably being from about 5% to about 90% and in particular from about 10% to about 90%.
The media according to the invention preferably include from about 1 to about 40%, particularly preferably from about 5 to about 30%, of compounds of the formula I. The media preferably include two or more compounds of the formula I.
The construction of the IPS displays according to the invention corresponds to the usual design of displays of this type, as described, for example, in WO 91/10936 or EP 0 588 568. The term xe2x80x9cconventional designxe2x80x9d is broadly drawn here and also covers all derivatives and modifications of the IPS display, in particular, for example, also matrix display elements based on poly-Si TFT or MIM.
However, an essential difference between the displays according to the invention and the displays conventional hitherto lies in the choice of the liquid-crystal parameters of the liquid-crystal layer.
The liquid-crystal mixtures which can be used in accordance with the invention are prepared in a manner which is customary per se. In general, the desired amount of the components used in the smaller amount are dissolved in the components making up the principal constituent, advantageously at elevated temperature. It is also possible to prepare the mixtures in other conventional manners, for example by using pre-mixtures, for example homologous mixtures, or using so-called xe2x80x9cmulti-bottlexe2x80x9d systems.
The dielectrics may also include further additives known to the person skilled in the art and described in the literature. For example, 0-about 15%, preferably 0-about 10%, of pleochroic dyes and/or chiral dopants can be added. The individual compounds added are employed in concentrations of from about 0.01 to about 6%, preferably from about 0.1 to about 3%. However, the concentration data for the other constituents of the liquid-crystal mixtures, i.e. the liquid-crystalline or mesogenic compounds, are given without taking into account the concentration of these additives.
Above and below, 
denote trans-1,4-cyclohexylene.
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.
In the foregoing and in the following examples, all temperatures are set forth uncorrected in degrees Celsius; and, unless otherwise indicated, all parts and percentages are by weight.
The entire disclosure[s] of all applications, patents and publications, cited above or below, and of corresponding German application No. 19919978.7, filed Apr. 30, 1999, is hereby incorporated by reference.